When comparing WinMerge vs DoubleKiller, the Slant community recommends WinMerge for most people. In the question“What are the best software tools to find duplicate files?” WinMerge is ranked 2nd while DoubleKiller is ranked 18th. The most important reason people chose WinMerge is:
You can quickly copy changed lines (or files in folder comparison) in both directions with keyboard shortcuts. You can edit the files as well, with syntax highlighting of some languages.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro File edition
You can quickly copy changed lines (or files in folder comparison) in both directions with keyboard shortcuts. You can edit the files as well, with syntax highlighting of some languages.
Pro Compare folders and files
Can show what files has been changed in a folder, allows comparing files in tabs.
Pro In line comparison
Can show differences within a line.
Pro Free & Open source
Winmerge is a free and open source tool.
Pro Good shell integration
Select two files and compare them. Alternatively, select one file, navigate elsewhere, select the other file to compare.
Also supports drag'n'drop of files / folders from Explorer.
History of past comparisons.
Pro Lightweight, quick startup
Binary is less than 3 MB, so it starts quickly
Pro Filters
Can filter out files for folder comparison, lines for file comparisons, with regular expressions.
Options also allow to ignore whitespace differences, white lines, case change, line-ending changes, etc.
Pro Good navigation
Keyboard shortcuts (and toolbar buttons) to navigate to next (previous) difference, side panel shows a map of the files with changed lines and allows to jump to a given place.
Pro Good detection of moved lines
Detects when a block of lines has been moved in the file and shows the relation.
Pro Tolerates multiple sessions
I often run multiple sessions of DoubleKiller Pro, to find duplicate files among different sets of disks.
Pro Flexible rules for finding duplicate files
The program can find duplicate files based on any combination of size, name, CRC, and byte-for-byte. It's possible to limit search to files matching a specific name or extension pattern (great for limiting search to certain file types) as well as using the same technique to exclude certain results. You can also tell the software to ignore any of combination of read only, hidden or system files as well as files of below or above certain size and archives.
Cons
Con Windows only
It's only available for Windows. No Mac or Linux versions available. It is possible to run in Linux via WINE, although a bit unstable.
Con Development is spotty
The latest version (2.16.0) was released in November 2018. Before that the last official release was made in 2013. The 2.16.0 is actually one of the two forks (Winmerge-v2-jp) that were kept maintained throughout the years, it just got named as the official release.
The other fork, WinMerge2011 is still being actively developed too. It's on par with the historical version, and has additional features such as showing only differences and a 64-bit version.
An 'official' list of forks is maintained here.
Con No 3-way merge
Cannot merge 3 files, can do only comparisons by pairs.
Makes it unsuitable for merging operations, still useful to compare two versions in the history.
Con No byte by byte comparison
While CRC checksums will be enough for most people, an option to check for duplicate files byte by byte would be nice.
[Edit] DoubleKiller does offer that option.
